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Patient for a follow up ultrasound two weeks after a lower pole renal transplant biopsy.

Caption:Color Doppler scan of the lower pole of the kidney

Description:An area of high velocity flow is revealed by the green area and is accompanied by a surrounding mosaic color pattern indicating focal tissue vibration.

Caption:Pulsed Doppler of the region of interest.

Description:An arterial waveform is noted showing elevated diastolic flow velocities [in the range of 80cm/s] as compared to the normal values [shown in the next image]. It can be inferred that there must be an abnormal communication of the artery with the vein.

Caption:Spectral analysis of the artery away from the region of interest.

Description:An arterial waveform is recorded with the low diastolic flow velocities [in the range of 10 cm/s] representing a normal renal arterial pattern.

Renal vascular complications following biopsy are more common in transplanted kidneys as compared to the native kidneys. Pseudoaneurysms and arterivenous fistulas are the most frequent complications. Color Doppler and spectral analysis are the initial methods of choice for the detection of these vascular lesions and are almost always diagnostic. These lesions usually pursue a benign course and close spontaneously, rarely requiring surgery. Intervention is required if the fistulas start to bleed forming perinephric collections or if they cause a vascular steal phenomenon.

According to various studies, the incidence of post biopsy arteriovenous fistulae range from 5- 10%. AV fistulae do not have any specific gray scale ultrasound diagnostic features. Color and pulsed Doppler features are characteristic. The region of the fistula has a high velocity blood flow which causes turbulence on color Doppler resulting in perivascular focal tissue vibration. This is demonstrated as a mosaic color pattern. Due to the anomalous connection with the vein, spectral analysis shows an abnormal low resistance arterial waveform with higher diastolic flow velocities. The venous flow pattern will also demonstrate an abnormal arterialized waveform due to increased flow in the vein. Also, 3D ultrasound angiography is emerging as an equally effective modality as MR angiography to demonstrate the exact location of the fistula and its orientation with respect to the other vascular structures.

Most of the studies conducted report spontaneous closure of these vessel abnormalities; however, a few cases may need angiography and embolization or surgical repair. It is suggested that post percutaneous needle biopsy in allograft kidneys periodical color Doppler of the allograft should be performed to detect asymptomatic pseudoaneurysms and AV fistulae. Most of these can then be simply followed up, unless the discussed complications supervene.